Polypeptides having NMDA receptor activity, nucleic acids encoding those polypeptides and applications

ABSTRACT

The present invention concerns novel polypeptides having NMDA receptor activity and genetic material permitting their expression. It also concerns a method for demonstrating and isolating ligands and/or modulators of the activity of these polypeptides and their utilization as drugs.

The present invention relates to new polypeptides and to the genetic material permitting their expression. More especially, it relates to new polypeptides having NMDA receptor activity.

Glutamic acid (glutamate) is a so-called excitatory amino acid, whose activity manifests itself in its interaction with specific receptors. Among these receptors, a subtype, designated NMDA (N-methyl-D-aspartate) receptors, appears to be implicated in the central nervous system of mammals, in many processes such as neuronal plasticity, long-term potentiation and also neuronal death or certain degenerative disorders. Pharmacological and molecular biology studies have recently made it possible to demonstrate and clone rat NMDA receptors, the receptor NMDAR1 [Moriyoshi et al., Nature 354 (1991) 31] and the receptor NMDAR2 [Monyer et al., Science 256 (1992) 12], and a mouse NMDA receptor [Yamazaki et al., Febs Lett. 300 (1992) 39].

The present invention is the outcome of the demonstration of new polypeptides having NMDA receptor activity. While belonging to the family of receptors associated with ion channels, these new polypeptides differ from the NMDA receptors already described from both a structural standpoint and a pharmacological standpoint. In particular, the receptors in question are of presynaptic origin, involved, in particular, in long-term potentiation (LTP).

More especially, the invention is the outcome of the isolation and characterization of new polypeptides, designated GR33, and also of the genetic material permitting their expression or identification. The invention also lies in the preparation of probes and of recombinant cells enabling the GR33 polypeptides to be exploited in diagnosis and the development of new active molecules.

A first subject of the invention hence lies in polypeptides comprising all or part of the peptide sequence SEQ ID No. 2 or of a derivative of the latter.

For the purposes of the present invention, the term derived denotes any molecule obtained by modification, of a genetic and/or chemical nature, of the peptide sequence SEQ ID No. 2. Modification of a genetic and/or chemical nature is understood to mean any mutation, substitution, deletion, addition and/or modification of one or more residues. Such derivatives may be generated for different purposes, such as, in particular, that of increasing the affinity of the peptide for its ligand(s), that of improving its levels of production, that of increasing its resistance to proteases, that of increasing and/or modifying its activity or that of endowing it with new pharmacokinetic and/or biological properties. Among derivatives resulting from an addition, chimeric polypeptides containing an additional heterologous portion attached at one end may, for example, be mentioned. The term derivative also comprises polypeptides homologous with the polypeptide SEQ ID No. 2, originating from other cell sources, and in particular from cells of human origin or of other organisms and possessing an activity of the same type. Such homologous polypeptides may be obtained by hybridization and/or PCR experiments, as described in the examples.

Preferably, the polypeptides of the invention are polypeptides possessing the capacity to bind glutamate. Still more preferably, they are polypeptides having NMDA receptor activity. Still according to a preferred embodiment, the polypeptides of the invention are capable of being recognized by antibodies which recognize the complete peptide sequence SEQ ID No. 2.

A particular embodiment of the invention is represented by the polypeptide GR33 comprising the whole peptide sequence SEQ ID No. 2. As shown in the examples, this polypeptide may be expressed in Xenopus eggs to form a functional glutamate receptor displaying all the pharmacological characteristics of an NMDA receptor:

the presence of 100 μM NMDA induces an inward current;

the absence of glycine from the medium inhibits the response to NMDA almost completely;

the responses to NMDA are reduced in the presence of competitive antagonists such as AP5 (D-2-amino-5-phosphonovaleric acid) or AP7 (D-2-amino-7-phosphonoheptanoic acid);

the NMDA concentration giving 50% of the maximum response (ED₅₀) is approximately 10 μM, corresponding to the values determined in the cases of the receptor NMDAR1;

among the other excitatory amino acids tested (glutamate, kainate, quisqualate, homocysteate), glutamate and homocysteate are those which induce the strongest responses.

Moreover, the results obtained show that the GR33 polypeptide comprising the whole peptide sequence SEQ ID No. 2 displays distinctive features relative to the other, known NMDA receptors. In particular, magnesium has only a partial inhibitory effect (30-70%) whereas it completely inhibits the activity of known NMDA receptors, and calcium has an inhibitory effect whereas it stimulates the activity of the NMDA receptors described. Furthermore, these distinctive pharmacological features are associated with distinctive structural features. In effect, the GR33 polypeptide SEQ ID No. 2, which comprises 288 amino acids and possesses a molecular weight of approximately 33 kDa, contains only a single hydrophobic domain (20 to 23 uncharged residues on the C-terminal side). This polypeptide also contains 2 potential glycosylation sites (Asn 115 and 134) and 4 cysteines which might be involved in the formation of secondary structures.

Another particular embodiment of the invention is represented by a polypeptide comprising the sequence presented in FIG. 1. This sequence corresponds to a fragment of a receptor homologous with the polypeptide SEQ ID No. 2, obtained from a human brain bank.

The polypeptides of the invention may be obtained by expression of a nucleotide sequence as described below in a cell host, by chemical synthesis on the basis of the given sequences SEQ ID No. 2 and FIG. 1 using techniques known to a person skilled in the art (solid- or liquid-phase peptide synthesis, and the like), or by a combination of these techniques.

In what follows, the polypeptides of the invention as defined above are designated GR33 polypeptides.

The subject of the present invention is also any nucleotide sequence coding for a GR33 polypeptide. More preferably, such a sequence is chosen from:

(a) all or part of the nucleotide sequence SEQ ID No. 1 or of its complementary strand,

(b) any sequence hybridizing with a sequence (a) and coding for a polypeptide as defined above, and

(c) the sequences derived from the sequences (a) and (b) as a result of the degeneracy of the genetic code.

The different nucleotide sequences of the invention can be of artificial origin or otherwise. They can be genomic, cDNA or RNA sequences, hybrid sequences or synthetic or semi-synthetic sequences. These sequences may be obtained, for example, by screening DNA libraries (cDNA library, genomic DNA library) by means of probes devised on the basis of the sequence SEQ ID No. 1. Such libraries may be prepared from cells of different origins by standard techniques of molecular biology known to a person skilled in the art. The nucleotide sequences of the invention may also be prepared by chemical synthesis, in particular according to the phosphoramidite method, or alternatively by mixed methods including the chemical or enzymatic modification of sequences obtained by screening libraries.

As an example of sequences hybridizing with a sequence (a) and coding for a polypeptide according to the invention, the sequence presented in FIG. 1 may be mentioned. Another example of a homologous sequence is represented by the human genomic clone described in FIG. 2, also isolated by hybridization.

The nucleotide sequences of the invention may be used for the production of GR33 polypeptides as defined above. In this case, the portion coding for the said polypeptide is generally placed under the control of signals permitting its expression in a cell host. The choice of these signals (promoters, terminators, and the like) can vary in accordance with the cell host used. To this end, the nucleotide sequences of the invention can form part of a vector, which can be an autonomously replicating or integrative vector. More especially, autonomously replicating vectors may be prepared using sequences which replicate autonomously in the chosen host. As regards integrative vectors, these may be prepared, for example, using sequences homologous with certain regions of the host's genome, permitting integration of the vector by homologous recombination. The cell hosts which are usable for the production of the GR33 polypeptides of the invention by the recombinant method are either eukaryotic or prokaryotic hosts. Among suitable eukaryotic hosts, animal cells, yeasts or fungi may be mentioned. In particular, as regards yeasts, yeasts of the genus Saccharomyces, Kluyveromyces, Pichia, Schwanniomyces or Hansenula may be mentioned. As regards animal cells, COS, CHO, C127 cells, Xenopus eggs, and the like, may be mentioned. Among fungi, Aspergillus ssp. or Trichoderma ssp. may be mentioned more especially. As prokaryotic hosts, it is preferable to use the following bacteria: E. coil, Bacillus or Streptomyces.

The nucleotide sequences of the present invention are also usable in the pharmaceutical field, either for the production of sense or antisense sequences which may be used in the context of a gene therapy, or else for the production of probes permitting the detection, by hybridization experiments, of the expression of NMDA receptors in biological samples, and the demonstration of genetic abnormalities (polymorphism, mutations) or of aberrant expressions.

Inhibition of the expression of certain genes by antisense oligonucleotides has proved to be a promising strategy in controlling the activity of a gene. Antisense oligonucleotides are small-sized oligonucleotides complementary to the coding strand of a given gene and, as a result, capable of hybridizing specifically with the transcribed mRNA inhibiting its translation into protein. A subject of the invention is thus antisense oligonucleotides capable of at least partially inhibiting the production of GR33 polypeptides. Such oligonucleotides can consist of all or part of the nucleotide sequences defined above. They are generally sequences or fragments of sequences complementary to sequences coding for peptides of the invention. Such oligonucleotides may be obtained from the sequence SEQ ID No. 1 or the sequence given in FIG. 1, by fragmentation, and the like, or by chemical synthesis. The sequences of the invention may also be used in gene therapy, incorporated in vectors, in particular viral vectors (adenoviruses, retroviruses, adeno-associated viruses, and the like).

As stated above, the invention also makes it possible to produce nucleotide probes, synthetic or otherwise, capable of hydriding with the nucleotide sequences defined above which code for GR33 polypeptides of the invention, or with the corresponding mRNAs. Such probes may be used in vitro as a diagnostic tool for detecting the expression of a GR33 glutamate receptor, or alternatively for demonstrating genetic abnormalities (incorrect splicing, polymorphism, point mutations, and the like). In view of the numerous activities of the glutamate receptors, the probes of the invention may thus enable neurological, cardiovascular or psychiatric disorders to be identified as being associated with GR33 receptors. These probes may also be used for demonstrating and isolating homologous nucleic acid sequences coding for GR33 polypeptides as defined above, from other cell sources and preferably from cells of human origin, as illustrated in the examples. The probes of the invention generally contain at least 10 bases, and they can contain as much as the whole of the sequence presented as SEQ ID No. 1 or in FIG. 1, or of their complementary strand. Preferably, these probes are labelled prior to their use. For this purpose, different techniques known to a person skilled in the art may be employed (radioactive or enzymatic labelling, and the like). The hybridization conditions under which these probes may be used are mentioned in the general cloning techniques below, as well as in the examples.

Another subject of the invention lies in polyclonal or monoclonal antibodies or antibody fragments directed against a GR33 polypetide as defined above. Such antibodies may be generated by methods known to a person skilled in the art, bearing in mind the teachings given in the present application. In particular, these antibodies may be prepared by (1) immunizing an animal against the GR33 polypeptide whose sequence is given as SEQ ID No. 2 or in FIG. 1, or any fragment or derivative of these, (2) withdrawing blood, and (3) isolating the antibodies. These antibodies may also be generated by preparing hybridomas according to techniques known to a person skilled in the art.

The antibodies thereby obtained may be used, in particular, for demonstrating and isolating homologous nucleic acid sequences coding for GR33 polypeptides as defined above, from other cell sources and preferably from cells of human origin, as illustrated in the examples. They may also be used for demonstrating and isolating GR33 polypeptides.

Another subject of the invention relates to recombinant cells capable of expressing at their surface one or more GR33 polypeptides. These cells may be obtained by introducing a nucleotide sequence as defined above, coding for a polypeptide of the invention, and then culturing the said cells under conditions for expression of the said sequence.

The recombinant cells according to the invention can be either eukaryotic or prokaryotic cells. Among suitable eukaryotic cells, animal cells, yeasts or fungi may be mentioned. In particular, as regards yeasts, yeasts of the genus Saccharomyces, Kluyveromyces, Pichia, Schwanniomyces, or Hansenula may be mentioned. As regards animal cells, COS, CHO, C127 cells, Xenopus eggs, and the like, may be mentioned. Among fungi, Aspergillus ssp. or Trichoderma ssp. may be mentioned more especially. As prokaryotic cells, it is preferable to use the following bacteria: E. coli, Bacillus or Streptomyces. The cells thereby obtained may be used to measure the ability of different molecules to behave as a ligand or as a modulator of the polypeptides of the invention. More especially, they may thus be used in a method for demonstrating and isolating ligands or modulators of the polypeptides of the invention, and more preferably glutamate agonists and antagonists.

Another subject of the invention hence relates to a method for demonstrating and/or isolating ligands of the polypeptides of the invention, according to which the following steps are carried out:

a molecule or a mixture containing different molecules, which are possibly unidentified, is brought into contact with a recombinant cell as described above, expressing at its surface a polypeptide of the invention, or with a membrane preparation of such a cell, under conditions permitting interaction between the said polypeptide of the invention and the said molecule should the latter possess an affinity for the said polypeptide, and

the molecules bound to the said polypeptide of the invention are detected and/or isolated.

In a particular embodiment, this method of the invention is suitable for demonstrating and/or isolating glutamate agonists and antagonists for the polypeptides of the invention.

Another subject of the invention relates to a method demonstrating and/or isolating modulators of the polypeptides of the invention, according to which the following steps are carried out:

a molecule or a mixture containing different molecules, which are possibly unidentified, is brought into contact with a recombinant cell as described above, expressing at its surface a polypeptide of the invention, or with a membrane preparation of such a cell, in the presence of glutamate, under conditions permitting interaction between the said polypeptide of the invention and glutamate, and

the molecules capable of modulating the activity of glutamate with respect to the said polypeptide of the invention are detected and/or isolated.

Another subject of the invention relates to the use of a ligand or modulator identified and/or obtained according to the method described above, as a medicinal product. Such ligands or modulators can, in effect, enable certain neurological, cardiovascular or psychiatric disorders associated with GR33 receptors to be treated.

The invention also relates to any medicinal product comprising as active principle at least one molecule which acts on a peptide of the invention. Preferably, the molecule is a ligand or a modulator identified and/or isolated according to the method described above.

Other advantages of the present invention will become apparent on reading the examples which follow, which are to be considered as illustrative and non-limiting.

LEGEND TO THE FIGURES

SEQ ID NOs: 1 and 2: Nucleotide and peptide sequences of the rat GR33 receptor.

FIG. 1: Fragment of the nucleotide (SEQ ID NO: 3) and peptide (SEQ ID NO: 4) sequence of the human GR33 receptor.

FIG. 2: Restriction map of the human genomic clone carrying a sequence homologous with the sequence SEQ ID No. 1. EV=EcoRV; EI=EcoR1; H=HindIll; P=PstI; S=SmaI; B=BamHI.

FIG. 3: Hydrophobicity profile of the GR33 polypeptide of 288 amino acids.

FIG. 4: Pharmacological and electrophysiological study of the GR33 polypeptide of 288 amino acids, SEQ ID No. 2. The results are expressed as % of the current induced by 200 μM NMDA alone. GLUT=glutamate; HCA=200 μM homocysteate; KA=300 mM kainate; QA=50 μM quisqualate; NM-gly=200 μM NMDA in the absence of glycine; NM+Mg=200 μM NMDA in the presence of 200 μM Mg²⁺ ; AP7=200 μM NMDA in the presence of 10 μM AP7. Each point represents a mean of at least 5 measurements performed on different Xenopus eggs.

FIG. 5: Demonstration of homologous sequences by Northern blotting on poly(A) mRNA (1 μg) of cerebellum (lane 1), cortex (lane 2), striatum (lane 3) and hippocampus (lane 4). The probe used corresponds to the complete cDNA SEQ ID No. 1.

FIG. 6: Demonstration of homologous polypeptides by Western blotting on synaptosomal membranes.

GENERAL CLONING TECHNIQUES

The methods traditionally used in molecular biology, such as preparative extractions of plasmid DNA, centrifugation of plasmid DNA in a caesium chloride gradient, agarose or acrylamide gel electrophoresis, purification of DNA fragments by electroelution, protein extractions with phenol or phenol/chloroform, ethanol or isopropanol precipitation of DNA in a saline medium, transformation in Escherichia coli, and the like, are well known to a person skilled in the art and are amply described in the literature [Maniatis T. et al., "Molecular Cloning, a Laboratory Manual", Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y., 1982; Ausubel F. M. et al. (eds), "Current Protocols in Molecular Biology", John Wiley and Sons, New York 1987].

Restriction enzymes were supplied by New England Biolabs (Biolabs), Bethesda Research Laboratories (BRL) or, Amersham, and are used according to the suppliers' recommendations.

Plasmids of the pBR322, pUC, λgt11 and pGEX type and phages of the M13 series are of commercial origin.

For ligation, the DNA fragments are separated according to size by agarose or acrylamide gel electrophoresis, extracted with phenol or with a phenol/chloroform mixture, precipitated with ethanol and then incubated in the presence of phage T4 DNA ligase (Biolabs) according to the supplier's recommendations.

The filling-in of 5' protruding ends is performed with the Klenow fragment of E. coli DNA polymerase I (Biolabs) according to the supplier's specifications. The destruction of 3' protruding ends is performed in the presence of phage T4 DNA polymerase (Biolabs) used according to the manufacturer's recommendations. The destruction of 5' protruding ends is performed by a controlled treatment with S1 nuclease.

Mutagenesis directed in vitro by synthetic oligodeoxynucleotides is performed according to the method developed by Taylor et al. [Nucleic Acids Res. 13 (1985) 8749-8764] using the kit distributed by Amersham.

The enzymatic amplification of DNA fragments by the so-called PCR [Polymerase-catalyzed Chain Reaction, Saiki R. K. et al., Science 230 (1985) 1350-1354; Mullis K. B. and Faloona F. A., Meth. Enzym. 155 (1987) 335-350] technique is performed using a "DNA thermal cycler" (Perkin Elmer Cetus) according to the manufacturer's specifications.

Verification of the nucleotide sequences is performed by the method developed by Sanger et al. [Proc. Natl. Acad. Sci. USA, 74 (1977) 5463-5467] using the kit distributed by Amersham.

For the hybridization experiments, the normal conditions of stringency are generally as follows: hybridization: 3×SCC in the presence of 5×Denhart's at 65° C.; washing: 0.5×SSC at 65° C.

1. Cloning of the cDNA H500 of FIG. 1

This example describes the cloning of an approximately 500-bp cDNA from human brain, coding for a portion of GR33 polypeptide. This cDNA was obtained by screening a human brain library by means of antibodies directed against glutamate-binding proteins.

1.1 Preparation of Purified Glutamate-Binding Proteins.

Synaptosomal membranes were prepared according to the technique described by Michaelis et al. [J. Neurochem. 42 (1984) 397] and solubilized in the presence of sodium deoxycholate. The membranes thus solubilized were then subjected to affinity chromatography on a glutamate column. The glutamate-binding proteins were eluted with 1M NaCl solution and dialysed against Tris-HCl buffer in the presence of 0.05% of sodium deoxycholate.

1.2. Production of Polyclonal Antibodies.

Polyclonal antibodies directed against the glutamate-binding proteins obtained above were prepared in mice. For this purpose, BALB/C mice were immunized with 50-100 μg of the glutamate-binding proteins obtained above, in the presence of Freund's complete adjuvant. Subsequent injections (every 8 to 10 days) were carried out with 50 μg of glutamate-binding proteins, but without Freund's complete adjuvant. After 5 injections, the sera were collected and stored frozen.

1.3. Screening of a Human Brain Library.

The antibodies prepared above were used to screen a human brain library produced in the vector lambda λgt11 (Clontech). Two million clones of this library were screened immunologically in this way, according to the technique described by Sambrook, Fritsch and Maniatis (see general cloning techniques). The positive clones identified were then purified to homogeneity by several successive screening steps. From these clones, an approximately 500-bp cDNA was obtained and sequenced on both strands. The sequence of this cDNA, designated H500, is presented in FIG. 1. No particular homology was found between this sequence and those available in the libraries.

2. Cloning of the cDNA Coding for the GR33 Polypeptide SEQ ID No.2

This example describes the cloning of an approximately 1.7-kb cDNA from rat brain, coding for the GR33 polypeptide SEQ ID No. 2. This cDNA was obtained by screening a rat brain library using radio-labelled cDNA H500 as probe.

The cDNA coding for the GR33 polypeptide SEQ ID No. 2 was obtained by screening a rat brain library constructed in the vector lambda ZAP (Stratagene). This library was screened with cDNA H500 previously labelled with ³² P by the "random priming" technique [Feinberg and Vogelstein, Analytical Biochemistry 132 (1984) 6}]. Hybridization was carried out under the following highly stringent conditions: hybridization at 65° C., 3-4×SSC, 5×Denhardt's, rinsing at 65° C., 0.1×SSC, 1% SDS. Approximately 1 million clones of the library were analysed in this way. One positive clone was isolated and purified. The plasmid carried by this clone was excised from the lambda ZAP DNA by means of a helper phage (Stratagene), and the 1.7-kb cDNA carried by this plasmid was sequenced on both strands. A portion of the sequence thereby obtained is presented in SEQ ID No. 1.

3. In Vitro Translation of the 1.7-kb cDNA

The 1.7-kb cDNA isolated above was translated in vitro in the rabbit reticulocyte system (Promega). This enabled an expressed protein having a molecular weight of approximately 35 kDA to be demonstrated. The protein deduced from the sequence SEQ ID No. 1 possesses a theoretical weight of 33.2 kDa. The hydrophobicity profile of the resulting protein of 288 amino acids was analysed according to the programme of Kyte and Doolittle [J. Molec. Biol. 157 (1982) 105]. The profile obtained is presented in FIG. 3. It indicates that the GR33 polypeptide comprising the whole sequence SEQ ID No. 2 possesses only one hydrophobic domain.

4. Expression of the GR33 Polypeptide SEQ ID No. 2 in Xenopus Eggs, and Pharmacological and Electrophysiological Study

The cDNA fragment isolated in Example 2 was transcribed into mRNA and microinjected into Xenopus eggs. The microinjected eggs thereby obtained were then tested for their capacity to bind certain labelled NMDA receptor ligands, or for their behaviour with respect to modulators of NMDA receptors.

4.1. In Vitro Transcription

The plasmid containing the 1.7-kb cDNA coding for the GR33 polypeptide SEQ ID No. 2 was linearized in the presence of the enzyme SmaI, and then subjected to a transcription step in the presence of phage T7 RNA polymerase. Transcription was performed using the Stratagene Kit according to the manufacturer's recommendations.

4.2. Microinjection

The synthetic RNA obtained above, dissolved in sterile water, was used (5 ng) for injection into mature Xenopus eggs (stages V and VI) in a volume of 50 nl. The eggs were then maintained for 3 days at 19° C. in multi well plates in a Barth medium supplemented with antibiotics (Miledi and Sumikawa, Biomed. Res. 3 (1982) 390).

4.3. Pharmacological and Electrophysiological Study

The eggs thereby obtained were then tested for the presence of functional NMDA receptors at their surface. For this purpose, the eggs were transferred to modified OR-2 medium lacking magnesium, of composition: 88 mM NaCl, 2.5 mM KCl, 1 mM CaCl₂, 10 mM HEPES buffer, pH 7.4 adjusted with sodium hydroxide. The different drugs (ligands or modulators) were applied by perfusion (10 ml/min) for 10-30 seconds under an applied potential difference of -80 or -90 mV. The results obtained are presented in FIG. 4. They show that:

the application of glutamate (0.1-1 mM) or of its agonist, NMDA (200 μM), induces an inward current, whereas other glutamate agonists including kainate (300 mM) and quisqualate (50 μM) have little or no effect. These results indicate that the injected eggs present at their surface glutamate receptors coupled to functional ion channels, of the NMDA type.

the response induced by NMDA (200 μM) is abolished when the medium does not contain glycine, or when the NMDA antagonists, AP5 or AP7, are applied (200 μM) simultaneously with NMDA. This result indicates that the response to NMDA of the injected eggs is pharmacologically comparable to that of a native NMDA receptor.

the response induced by NMDA (200 μM) is decreased when magnesium (200 μM) is added to the medium, or when there is an increase in the external calcium concentration (2.5 mM).

5. Search for Homologous Nucleotide Sequences and Polypeptides in Other Tissues

The nucleotide sequence SEQ ID No. 1 was then used as probe for demonstrating homologous sequences on other tissues. For this purpose, two techniques were used:

Northern blot hybridization,

in situ hybridization.

The tissues used to search for homologous sequences are the following ones of murine origin: cerebellum, cortex, striatum, hippocampus.

5.1. Search by Northern Blotting

Poly(A) mRNAs were prepared from the tissues mentioned above according to the guanidinium isothiocyanate technique described by Chirgwin et al. [Biochemistry 18 (1979) 5294], followed by passage through an oligo(dT)-cellulose column. These mRNAs were then fractionated on agarose gel and thereafter transferred onto nylon membranes (Hybond N+). The probe used for hybridization corresponds to the whole 1.7-kb cDNA described in Example 2 (SEQ ID No. 1), previously labelled with ³² P according to the technique described by Maniatis et al. (see general cloning techniques). Hybridization with the different tissues was carried out under highly stringent conditions: hybridization at 42° C., 6×SSC, 50% formamide, 1×Denhardt's, rinsing at 65° C., 0.1×SSC, 1% SDS.

This study enabled homologous specific DNA fragments to be demonstrated in all the tissues studied (FIG. 5).

5.2. Search by In Situ Hybridization

In situ hybridization experiments were carried out on cryostat sections of rat brain according to the technique described by Hafen et al. [EMBO J. 2 (1983) 617]. The probe used for these experiments corresponds to the whole 1.7-kb cDNA described in Example 2 (SEQ ID No. 1) previously labelled by means of digoxigenin-labelled deoxyuridine triphosphate (dig-U, Boehringer Mannheim) according to the technique described by Dumas et al. [J. Neurosci. Res. 25 (1990) 569]. This non-radioactive labelling and also the detection of the hybrids were carried out by immunoenzymatic testing using anti-digoxigenin antibodies conjugated to alkaline phosphatase, which are visualized in the presence of a chromogenic substrate for the enzyme, 5-bromo-4-chloro-3-indolyl phosphate, and nitro blue tetrazolium salt, following the recommendations of the manufacturer (Boehringer Mannheim). Hybridization with the different tissues was carried out under highly stringent conditions: hybridization at 42° C., 6×SSC, 50% formamide, 1×Denhardt's, rinsing at 65° C., 0.1×SSC, 1% SDS.

This study enabled homologous sequences according to the invention to be demonstrated, in particular in Purkinje cells and in granular cells of the cerebellum, in pyramidal cells of the CA1 and CA3 regions of the hippocampus and in some regions of the cortex.

It is understood that the same experiments may be repeated using other tissues, and in particular tissues of human origin, and other probes. Moreover, the homologous sequences demonstrated in these experiments may naturally be isolated and/or amplified thereafter by standard techniques of molecular biology.

6. Use of Anti-GR33 Polypeptides Antibodies for Demonstrating Homologous Nucleotide Sequences and Polypeptides in Other Tissues

Polyclonal anti-GR33 polypeptides antibodies were prepared and used for demonstrating homologous polypeptides on other tissues by Western blot experiments.

6.1. Preparation of Antibodies

A cDNA fragment containing the region coding for the GR33 polypeptide SEQ ID No. 1 described in Example 2 was generated by PCR by means of the following specific oligonucleotides:

    TAATACGACTCACTATAGGATCCGACCCCGGCCTCCAGCA (SEQ ID NO: 5)    (i)

    GCAATTAACCCTCACTAAAGAATTCCCGATGTGTGGGGAGG (SEQ ID NO: 6)   (ii)

These oligonucleotides correspond to positions 124 and 1104, respectively, in the sequence SEQ ID No. 1.

The product of this amplification was then subcloned into the E. coli expression vector pGEX-2 [Smith and Johnston, Gene 67 (1988) 31] so as to permit its expression in the form of a fusion protein with glutathione S-transferase (GST-GR33). The fusion protein thereby produced was then purified and used as antigen for preparing antibodies in rabbits. For this purpose, rabbits were immunized with 50-100 μg of antigen in the presence of Freund's complete adjuvant. After 3 weeks, a further injection was carried out with 50 μg of antigen, but without Freund's complete adjuvant. After 2 injections, sera were collected and stored frozen.

6.2. Demonstration of Homologous Sequences

Synaptosomal membranes were prepared according to the technique described by Michaelis et al. [J. Neurochem. 42 (1984) 397] and solubilized in the presence of 0.5% sodium deoxycholate. Approximately 50 μg of proteins thereby obtained were subjected to an electrophoretic analyses on 10% SDS gel. The proteins were then transferred onto nitrocellulose and brought into contact with the antibodies prepared in 6.1. above. The bound antibodies were then visualized by means of the ECL detection system (Amersham).

As seen in FIG. 6, this study enabled different polypeptides comprising all or part of the peptide sequence SEQ ID No. 2 and having molecular weights of 35 kDa, 69-70 kDa, 97-98 kDa and 110 kDa approximately, to be demonstrated in synaptosomal membranes.

7. Isolation and Characterization of a Human Genomic Clone Coding for a GR33 Polypeptide

This example describes the isolation and characterization of a human genomic clone coding from a GR33 polypeptide. This clone was obtained by screening a human library using radio labelled cDNA H500 as probe.

The human clone of FIG. 2 was obtained by screening a human genomic library constructed in the vector lambda EMBL3 (Clontech). This library contains approximately 13-kb genomic inserts inserted into the SaII site of the vector lambda EMBL3. This library was screened with cDNA H500 previously labelled with ³² P by the "random priming" technique [Feinberg and Vogelstein, Analytical Biochemistry 132 (1984) 6]. Hybridization was carried out under the following highly stringent conditions: hybridization at 65° C., 3-4×SSC, 5×Denhardt's, rinsing at 65° C., 0.1×SSC, 1% SDS. Approximately 2×10⁵ clones of the library were analysed in this way. One positive clone was isolated and purified. The plasmid thereby obtained (E17) carries an approximately 12-kb genomic insert, a restriction map of which is presented in FIG. 3. The sequence coding for the GR33 polypeptide is located in the 3' 6.5-kb HindIll-PstI fragment of plasmid E17.

    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 6                                                   (2) INFORMATION FOR SEQ ID NO:1:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1200 base pairs                                                    (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: double                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: cDNA                                                       (iii) HYPOTHETICAL: NO                                                         (iv) ANTI-SENSE: NO                                                            (ix) FEATURE:                                                                  (A) NAME/KEY: CDS                                                              (B) LOCATION: 211..1077                                                        (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                        ATTCCGGGCAGCCTAGGCAGAGCCAGTCGGCCCAGGCCCCTGTCTCTGCCTGGCCTCAGC60                 TCCCCGCCCCCCCGCCGCGCACCTTACCCGCACATCCCTCGGAGGTCTAGCCGGGTGCCC120                CCAGACCCCGGCCTCCAGCACAGAGGCAAGAGGCAGAGAGCAGCAGCGGAGGCGGGAGGA180                CGAAGAAGGGGAGGAGGAGCCCGTCGCAGGATGAAGGATCGGACTCAGGAGCTG234                      MetLysAspArgThrGlnGluLeu                                                       15                                                                             CGGAGTGCAAAAGACAGTGACGATGAAGAGGAAGTGGTTCATGTGGAT282                            ArgSerAlaLysAspSerAspAspGluGluGluValValHisValAsp                               101520                                                                         CGAGACCACTTTATGGATGAGTTCTTTGAGCAGGTGGAAGAGATCCGA330                            ArgAspHisPheMetAspGluPhePheGluGlnValGluGluIleArg                               25303540                                                                       GGCTGCATCGAGAAACTGTCCGAGGATGTGGAGCAAGTGAAGAAACAG378                            GlyCysIleGluLysLeuSerGluAspValGluGlnValLysLysGln                               455055                                                                         CACAGTGCCATTCTTGCTGCCCCCAACCCCGATGAGAAGACTAAACAG426                            HisSerAlaIleLeuAlaAlaProAsnProAspGluLysThrLysGln                               606570                                                                         GAGCTGGAGGACCTCACGGCAGACATCAAAAAGACGGCAAACAAGGTC474                            GluLeuGluAspLeuThrAlaAspIleLysLysThrAlaAsnLysVal                               758085                                                                         CGGTCCAAGTTGAAAGCGATCGAGCAGAGCATTGAGCAGGAAGAGGGG522                            ArgSerLysLeuLysAlaIleGluGlnSerIleGluGlnGluGluGly                               9095100                                                                        TTGAATCGTTCTTCTGCAGACCTGCGTATCCGTAAGACCCAGCACTCC570                            LeuAsnArgSerSerAlaAspLeuArgIleArgLysThrGlnHisSer                               105110115120                                                                   ACACTCTCACGGAAGTTCGTGGAGGTAATGACCGAATATAATGCAACT618                            ThrLeuSerArgLysPheValGluValMetThrGluTyrAsnAlaThr                               125130135                                                                      CAGTCTAAGTACCGGGACCGCTGCAAGGACCGTATCCAGAGGCAGCTG666                            GlnSerLysTyrArgAspArgCysLysAspArgIleGlnArgGlnLeu                               140145150                                                                      GAGATCACTGGCAGGACTACTACCAACGAAGAGCTGGAAGACATGTTG714                            GluIleThrGlyArgThrThrThrAsnGluGluLeuGluAspMetLeu                               155160165                                                                      GAAAGCGGGAAGCTGGCCATCTTCACGGACGACATCAAAATGGACTCG762                            GluSerGlyLysLeuAlaIlePheThrAspAspIleLysMetAspSer                               170175180                                                                      CAGATGACAAAGCAAGCCCTGAATGAGATAGAGACAAGGCACAATGAG810                            GlnMetThrLysGlnAlaLeuAsnGluIleGluThrArgHisAsnGlu                               185190195200                                                                   ATCATCAAACTGGAAACCAGCATCCGAGAGCTGCACGACATGTTTGTG858                            IleIleLysLeuGluThrSerIleArgGluLeuHisAspMetPheVal                               205210215                                                                      GACATGGCCATGCTCGTGGAGAGCCAGGGTGAGATGATCGACCGAATT906                            AspMetAlaMetLeuValGluSerGlnGlyGluMetIleAspArgIle                               220225230                                                                      GAGTACAATGTGGAACATTCTGTGGACTACGTGGAGCGAGCCGTGTCC954                            GluTyrAsnValGluHisSerValAspTyrValGluArgAlaValSer                               235240245                                                                      GACACCAAGAAAGCTGTGAAATATCAGAGCAAGGCCAGGAGGAAGAAA1002                           AspThrLysLysAlaValLysTyrGlnSerLysAlaArgArgLysLys                               250255260                                                                      ATTATGATCATCATTTGCTGTGTGGTGCTGGGGGTGGTCTTGGCGTCA1050                           IleMetIleIleIleCysCysValValLeuGlyValValLeuAlaSer                               265270275280                                                                   TCTATTGGGGGGACACTGGGCTTGTAGGCCCCTACCCTTCTCTTCCCCAGGACC1104                     SerIleGlyGlyThrLeuGlyLeu                                                       285                                                                            CTCCCCACACATCGGGAGCAATACCCCCACCACCCTTTCACTCTTTCCCCTGCTCCAAGC1164               TCACTCCCAAAACAGACCCAGGCAGTTCCAGCCTCT1200                                       (2) INFORMATION FOR SEQ ID NO:2:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 288 amino acids                                                    (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                        MetLysAspArgThrGlnGluLeuArgSerAlaLysAspSerAspAsp                               151015                                                                         GluGluGluValValHisValAspArgAspHisPheMetAspGluPhe                               202530                                                                         PheGluGlnValGluGluIleArgGlyCysIleGluLysLeuSerGlu                               354045                                                                         AspValGluGlnValLysLysGlnHisSerAlaIleLeuAlaAlaPro                               505560                                                                         AsnProAspGluLysThrLysGlnGluLeuGluAspLeuThrAlaAsp                               65707580                                                                       IleLysLysThrAlaAsnLysValArgSerLysLeuLysAlaIleGlu                               859095                                                                         GlnSerIleGluGlnGluGluGlyLeuAsnArgSerSerAlaAspLeu                               100105110                                                                      ArgIleArgLysThrGlnHisSerThrLeuSerArgLysPheValGlu                               115120125                                                                      ValMetThrGluTyrAsnAlaThrGlnSerLysTyrArgAspArgCys                               130135140                                                                      LysAspArgIleGlnArgGlnLeuGluIleThrGlyArgThrThrThr                               145150155160                                                                   AsnGluGluLeuGluAspMetLeuGluSerGlyLysLeuAlaIlePhe                               165170175                                                                      ThrAspAspIleLysMetAspSerGlnMetThrLysGlnAlaLeuAsn                               180185190                                                                      GluIleGluThrArgHisAsnGluIleIleLysLeuGluThrSerIle                               195200205                                                                      ArgGluLeuHisAspMetPheValAspMetAlaMetLeuValGluSer                               210215220                                                                      GlnGlyGluMetIleAspArgIleGluTyrAsnValGluHisSerVal                               225230235240                                                                   AspTyrValGluArgAlaValSerAspThrLysLysAlaValLysTyr                               245250255                                                                      GlnSerLysAlaArgArgLysLysIleMetIleIleIleCysCysVal                               260265270                                                                      ValLeuGlyValValLeuAlaSerSerIleGlyGlyThrLeuGlyLeu                               275280285                                                                      (2) INFORMATION FOR SEQ ID NO:3:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 477 base pairs                                                     (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: double                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: cDNA                                                       (iii) HYPOTHETICAL: NO                                                         (iv) ANTI-SENSE: NO                                                            (vi) ORIGINAL SOURCE:                                                          (A) ORGANISM: Homo sapiens                                                     (ix) FEATURE:                                                                  (A) NAME/KEY: CDS                                                              (B) LOCATION: 2..475                                                           (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                        GTTCTTTGAACAGGTGGAAGAGATCCGAGGCTGCATTGAGAAACTG46                               PhePheGluGlnValGluGluIleArgGlyCysIleGluLysLeu                                  151015                                                                         TCGGAGGATGTGGAGCAGGTGAAAAAACAGCATAGCGCCATCCTGGCC94                             SerGluAspValGluGlnValLysLysGlnHisSerAlaIleLeuAla                               202530                                                                         GCACCCAACCCAGATGAGAAGACCAAACAGGAGCTGGAGGATCTCACT142                            AlaProAsnProAspGluLysThrLysGlnGluLeuGluAspLeuThr                               354045                                                                         GCAGACATCAAGAAGACGGCCAACAAGGTTCGGTCCAAATTGAAAGCG190                            AlaAspIleLysLysThrAlaAsnLysValArgSerLysLeuLysAla                               505560                                                                         ATCGAGCAAAGCATTGAACAGGAGGAGGGGCTGAACCGTTCCTCCGCG238                            IleGluGlnSerIleGluGlnGluGluGlyLeuAsnArgSerSerAla                               657075                                                                         GACCTGCGCATCCGCAAGACCCAGCACTCCACACTGTCCCGGAAGTTC286                            AspLeuArgIleArgLysThrGlnHisSerThrLeuSerArgLysPhe                               80859095                                                                       GTGGAGGTAATGACCGAATATAACGCGACCCAGTCCAAGTACCGGGAC334                            ValGluValMetThrGluTyrAsnAlaThrGlnSerLysTyrArgAsp                               100105110                                                                      CGCTGCAAGGACCGGATCCAGCGGCAACTGGAGATCACTGGAAGGACC382                            ArgCysLysAspArgIleGlnArgGlnLeuGluIleThrGlyArgThr                               115120125                                                                      ACCACCAACGAAGAACTGGAAGACATGCTGGAGAGCGGGAAGCTGGCC430                            ThrThrAsnGluGluLeuGluAspMetLeuGluSerGlyLysLeuAla                               130135140                                                                      ATCTTCACAGATGACATCAAAATGGACTCACAGATGACGAAACAG475                               IlePheThrAspAspIleLysMetAspSerGlnMetThrLysGln                                  145150155                                                                      GC477                                                                          (2) INFORMATION FOR SEQ ID NO:4:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 158 amino acids                                                    (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                        PhePheGluGlnValGluGluIleArgGlyCysIleGluLysLeuSer                               151015                                                                         GluAspValGluGlnValLysLysGlnHisSerAlaIleLeuAlaAla                               202530                                                                         ProAsnProAspGluLysThrLysGlnGluLeuGluAspLeuThrAla                               354045                                                                         AspIleLysLysThrAlaAsnLysValArgSerLysLeuLysAlaIle                               505560                                                                         GluGlnSerIleGluGlnGluGluGlyLeuAsnArgSerSerAlaAsp                               65707580                                                                       LeuArgIleArgLysThrGlnHisSerThrLeuSerArgLysPheVal                               859095                                                                         GluValMetThrGluTyrAsnAlaThrGlnSerLysTyrArgAspArg                               100105110                                                                      CysLysAspArgIleGlnArgGlnLeuGluIleThrGlyArgThrThr                               115120125                                                                      ThrAsnGluGluLeuGluAspMetLeuGluSerGlyLysLeuAlaIle                               130135140                                                                      PheThrAspAspIleLysMetAspSerGlnMetThrLysGln                                     145150155                                                                      (2) INFORMATION FOR SEQ ID NO:5:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 40 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: other nucleic acid                                         (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                        TAATACGACTCACTATAGGATCCGACCCCGGCCTCCAGCA40                                     (2) INFORMATION FOR SEQ ID NO:6:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 41 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: other nucleic acid                                         (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:                                        GCAATTAACCCTCACTAAAGAATTCCCGATGTGTGGGGAGG41                                    __________________________________________________________________________ 

We claim:
 1. An isolated polypeptide comprising a sequence selected from the group consisting of:(a) SEQ ID No. 2, (b) SEQ ID No. 4, and (c) a fragment of (a) or (b) wherein said fragment has NMDA receptor activity.
 2. A polypeptide according to claim 1, characterized in that it possesses the capacity to bind glutamate.
 3. A polypeptide according to claim 2, characterized in that it possesses NMDA receptor activity.
 4. A polypeptide according to claim 1, characterized in that it can be recognized by antibodies which recognize the complete peptide sequence SEQ ID No.
 2. 5. A polypeptide according to claim 4, characterized in that it is selected from the group consisting of polypeptides having a molecular weight of 35 kDa, 69-70 kDa, 97-98 kDa and 110 kDa described in FIG.
 6. 6. A polypeptide according to claim 1, characterized in that it comprises the sequence SEQ ID No.
 2. 7. A polypeptide according to claim 1, characterized in that it comprises the sequence SEQ ID No.
 4. 8. An recombinant nucleic acid encoding for a polypeptide, wherein said polypeptide comprises an amino acid sequence selected from the group consisting of;(a) SEQ ID NO: 2 (b) SEQ ID NO: 4 and (c) a fragment of (a) or (b) wherein said fragment has NMDA receptor activity.
 9. A nucleic acid according to claim 8, comprising a sequence selected from the group consisting of:(a) SEQ ID No. 1, (b) sequences which hybridize with (a) under highly stringent conditions, and (c) sequences derived from (a) and (b) as a result of the degeneracy of the genetic code.
 10. A nucleic acid according to claim 8, comprising a sequence selected from the group consisting of:(a) SEQ ID No. 3, (b) sequences which hybridize with (a) under highly stringent conditions, and (c) sequences derived from (a) and (b) as a result of the degeneracy of the genetic code.
 11. A nucleic acid according to claim 8, wherein said nucleic acid is placed under the control of signals permitting its expression in a host cell.
 12. A recombinant cell comprising a nucleic acid according to claim
 8. 13. A cell according to claim 12, selected from the group consisting of eukaryotic cells and prokaryotic cells.
 14. A vector comprising the nucleic acid of claim
 8. 15. A pharmaceutical composition comprising a vector according to claim
 14. 16. An isolated nucleic acid encoding a polypeptide, wherein said polypeptide comprises an amino acid sequence selected from the group consisting of;(a) SEQ ID NO: 2 (b) SEQ ID NO: 4 and (c) a fragment of (a) or (b) wherein said fragment has NMDA receptor activity; and wherein said nucleic acid is selected from the group consisting of genomic DNA, cDNA, RNA, hybrid nucleic acids, synthetic nucleic acids and semi-synthetic nucleic acids. 